Organization of cells in the inner ear enables the sense and sensitivity of hearing

May 14, 2018, Massachusetts Eye and Ear Infirmary
Depiction of the inner ear, with a stylized glimpse inside at the vibrating lattice of 'Y-shaped' cellular architecture found within the organ of Corti. Credit: Hamid Motallebzadeh, Garyfallia Pagonis, Peter Gottlieb, Haobing Wang, and Sunil Puria of Mass. Eye and Ear

The loss of tiny cells in the inner ear, known as "hair cells," is a leading cause of hearing loss, a public health problem affecting at least one out of three people over the age of 65. Of the two varieties of hair cells, the "outer hair cells" act as micromotors that amplify incoming sound, and the "inner hair cells" act to sense and transmit information about the sound to the brain. Hair cells do not regenerate on their own in human ears, and they can die away from a variety of factors including excessive noise exposure, certain medications, infection and as part of the natural aging process.

Researchers around the world are working to restore human hearing by regenerating outer in the cochlea of the inner ear, the loss of which is a leading cause of hearing impairment, through a variety of techniques, and some have even shown success in restoring some hearing sensitivity in animal studies. However, new research shows that restoring hearing is not just about regenerating the lost outer hair cells. In a study published online today in the journal Proceedings of the National Academy of Sciences (PNAS), a research team from Mass. Eye and Ear has shown that, in order to effectively amplify and tune sound, each of the outer hair cells must be arranged as a specific branch of a Y-shaped building block, which is replicated thousands of times within the cochlea to form a highly organized cellular architecture.

"Our work suggests that, in order for humans to hear well, the outer hair cells in the cochlea not only need to be in good working order, but also need to be connected to other nearby cochlear structures in a very particular way," said senior author Sunil Puria, Ph.D., an Amelia Peabody Scientist at Mass. Eye and Ear and instructor in otolaryngology at Harvard Medical School. "It had been assumed that, if we could just succeed in regenerating outer hair cells, it would be sufficient to restore hearing. But our work shows that the spatial organization of the restored cells must also be taken into account."

Motivated by previous studies in their lab, the researchers created a detailed computer simulation of the cochlea and the tiny structures within it. They then tested how different arrangements and malformations of the Y-shaped structures affect hearing function. They found that the outer hair cells could only produce high hearing sensitivity and frequency selectivity when arranged in their natural configuration with respect to the surrounding structures. When they altered the geometry and material properties of these structures, the cells' ability to amplify and tune sound was compromised.

The study provides an important step toward understanding the functional implications of how the are arranged in the inner ear—with far-reaching implications for emerging new clinical therapies that aim to restore by regenerating these cells, but not necessarily in a way that restores their critical position within the natural Y-shaped building blocks of the cochlea.

"We built our model to test whether rearranging the cells in the Y-shaped structures of the inner ear alters the ear's ability to amplify sound," said Dr. Puria. "By altering these structures in the model, we see strong evidence that amplification and tuning in the cochlea depend heavily on the natural arrangement of these structures."

According to co-author Hamid Motallebzadeh, Ph.D., a postdoctoral fellow at Mass. Eye and Ear, "Computational models such as the one developed for this study can be used to replicate and interpret experimental measurements, thus potentially reducing the need for animal-based studies, and can also allow researchers to conduct well-controlled 'virtual experiments' that go far beyond what is currently possible to perform in actual experiments."

Explore further: Simple treatment may minimize hearing loss triggered by loud noises

More information: Hamid Motallebzadeh el al., "Cochlear amplification and tuning depend on the cellular arrangement within the organ of Corti," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1720979115

Related Stories

Simple treatment may minimize hearing loss triggered by loud noises

May 7, 2018
It's well known that exposure to extremely loud noises—whether it's an explosion, a firecracker or even a concert—can lead to permanent hearing loss. But knowing how to treat noise-induced hearing loss, which affects ...

Researchers discover how the brain balances hearing between our ears

May 12, 2015
UNSW researchers have answered the longstanding question of how the brain balances hearing between our ears, which is essential for localising sound, hearing in noisy conditions and for protection from noise damage.

Sensory hair cells regenerated, hearing restored in mammal ear

January 9, 2013
Hearing loss is a significant public health problem affecting close to 50 million people in the United States alone. Sensorineural hearing loss is the most common form and is caused by the loss of sensory hair cells in the ...

New technique generates high volume of sensory cells needed for hearing

February 21, 2017
The loss of tiny, sound-sensing cells in the inner ear, known as "hair cells," is a leading cause of hearing loss, a public health problem affecting at least 5 percent of the world population. Hair cells, which do not regenerate ...

Researcher describes cochlear amplification using novel optical technique

December 12, 2012
It has long been known that the inner ear actively amplifies sounds it receives, and that this amplification can be attributed to forces generated by outer hair cells in the cochlea.  How the ear actually accomplishes this, ...

New images reveal how the ear's sensory hairs take shape

February 9, 2018
Our ears are exquisite detection instruments, capable of discerning a whisper or distinct notes of music within a symphony. To pick up these sounds, tiny hair-like filaments in the inner ear must be packed into precisely ...

Recommended for you

Robots grow mini-organs from human stem cells

May 17, 2018
An automated system that uses robots has been designed to rapidly produce human mini-organs derived from stem cells. Researchers at the University of Washington School of Medicine in Seattle developed the new system.

Scientists uncover a new face of a famous protein, SWI2/SNF2 ATPase

May 17, 2018
A team of Texas A&M and Texas A&M AgriLife Research scientists now have a deeper understanding of a large switch/sucrose non-fermentable (SWI/SNF) protein complex that plays a pivotal role in plant and human gene expression ...

Antibacterial in your toothpaste may combat severe lung disease

May 17, 2018
A common antibacterial substance found in toothpaste may combat life-threatening diseases such as cystic fibrosis, or CF, when combined with an already FDA-approved drug.

Blocking two enzymes could make cancer cells mortal

May 17, 2018
EPFL scientists have identified two enzymes that protect chromosomes from oxidative damage and shortening. Blocking them might be a new anticancer strategy for stopping telomerase, the enzyme that immortalizes tumors.

Emergency contact information helps researchers branch out family tree

May 17, 2018
When you go to the doctor or hospital, one piece of information that you're always asked to provide—in addition to your name, address, and insurance information—is an emergency contact. Often, that person is a blood relative. ...

Study identifies bacterial gene responsible for producing enzyme that consumes cardiac drug

May 17, 2018
Though digoxin has been widely prescribed for decades to treat a variety of heart conditions, doctors have also long understood that, for some patients, the drug simply doesn't work.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.